Source: IBM.

Once upon a time, IBM (IBM 0.16%) and Apple (AAPL 0.64%) competed intensely in the consumer PC market. The rivalry was probably best captured in the famous photo of Steve Jobs making a rather unsavory gesture toward Big Blue. But that was decades ago, and after IBM officially exited the consumer PC market over 10 years ago to focus on enterprise software and analytics, Apple no longer had a reason to despise the company.

Quite the contrary, a year ago the two companies forged an important partnership, whereby IBM would create custom mobile apps tailored to specific enterprise verticals, while also selling iPhones and iPads to its broad base of enterprise customers. The partnership leverages both companies' strengths, and both should start seeing benefits soon.

It turns out that the pair are now taking their relationship to the next level, and IBM is perhaps turning into Apple's greatest ally in the enterprise market.

IBM wants you to use a Mac at Work
Earlier this week, IBM announced a handful of new Mac at Work services, where it would help enterprise customers securely integrate Macs into their systems, applications, and IT infrastructure. Big Blue mentions that it's already been helping clients adopt Macs in the enterprise, but up until now it's been more of a custom offering. Now it will be a standard offering, since enterprise interest in Macs continues to rise.

Source: Apple.

In fact, IBM began offering its own employees a choice between using a Mac or Microsoft Windows PC just a few months ago, whenever those employees were eligible to upgrade their workstations, as part of a new Mac@IBM. Ironically, IBM is encouraging employees to switch to Macs from Thinkpads, the PC brand that it sold to Lenovo in 2004.

At the time, IBM was already supporting approximately 15,000 Macs through its BYOD program, and it's expected to purchase about 50,000 additional Macs by year's end. That's a notable chunk of IBM's total employee count of around 380,000 as of the end of 2014.

IBM's chief information officer, Jeff Smith, met with Apple to express his interest in deploying more Macs at IBM but said the company would need some collaboration on Apple's part. The executive wants to bring the overall cost of deploying Macs down to equal or less than the cost of deploying PCs. Always the secretive one, Apple initially didn't want to play ball, since it could require giving IBM greater access to internal resources. Smith then asked what Apple's largest enterprise deployment was, and the answer was around 25,000. Smith then told Apple that IBM might purchase between 150,000 and 200,000 Macs and estimates that eventually 50% to 75% of employees would probably pick Macs, which immediately got the Mac maker's attention.

Tim Cook flew down the following week.

Everyone is doing it
As Big Blue builds experience with its own large-scale Mac deployment in the coming years, it will turn around and leverage that experience to help its own enterprise customers do likewise, since there is growing interest in Macs at the workplace.

Mark Zuckerberg uses a MacBook at work. Source: Facebook.

Macs have been on a slow but steady rise in the enterprise because of BYOD programs (even Fool HQ recently started offering Macs as part of a pick-your-own-device, or PYOD, program), so companies are starting to embrace the idea. As the Mac continues to gain consumer market share, those gains are inevitably starting to bleed into the enterprise as IT policies evolve.

This isn't just start-ups, either. For example, there are more MacBooks in use at Facebook than Windows PCs -- so much so that Facebook even writes its own custom OS X enterprise security software and then even open sources that software.

Keep your friends close, and IBM even closer
The Mac is doing quite literally better than ever. Even though Windows still towers over OS X on a global scale, Apple has made steady progress, gaining market share every year for the past decade. Apple shipped a record 5.5 million Macs in each of the third and fourth quarters last year.

Apple used to historically shy away from the enterprise market, in part because the purchaser (IT executives) was usually not the same as the user (employee), but the company seems much more interested in pursuing the immense opportunity there now. While it may take longer since enterprise upgrade cycles tend to be longer, Apple now has a very influential friend whispering into the ears of thousands of enterprise customers and decision makers, telling them why a Mac might be the way to go.